If I were you, I'd keep the 3690P. It's much rarer than the 3940, which means I can find another 3940 easily if I want to add it back to my collection in future. My 2 cents.
The 3960P is rarer (30 vs approx 600 pieces of 3940R, but you have a 3941 or 3940 second series with the early subdials which is much rarer than 600 pieces). The 3940R is more complex and special. Ideal combination, also with regards to the two different ...